1. Field of the Invention
The invention relates to an image forming apparatus and an image forming method used for a copy machine, a printer, a facsimile, and the like.
2. Description of Related Art
There is known an image forming system, the system using an intermediate transfer member, in which a transfer process of transferring a toner image from an electrophotographic photoreceptor (hereinafter, also referred to merely as ‘photoreceptor’) to a recording material incorporates another transfer process, wherein the toner image is primarily transferred from the electrophotographic photoreceptor to the intermediate transfer member, then the primary transfer image in the intermediate transfer member is secondarily transferred to the recording member, thereby the image forming system obtaining a final image. An intermediate transfer system as described above is mostly employed as a superimposing transfer system that superimposes toner images of respective colors in a so-called full color image forming apparatus, wherein the superimposing transfer system reproduces an original image, the original image having been color-separated, with use of a subtractive mixture of toners of black, cyan, magenta, yellow, etc.
However, when a large number of document sheets is copied or printed, toner filming occurs on an electrophotographic photoreceptor and an intermediate transfer member; the surface energy of the electrophotographic photoreceptor and the intermediate transfer member grows and the adhesion force to toner increases; transferability of the toner from the electrophotographic photoreceptor or the intermediate transfer member to a recording material is reduced; and thus, image defects easily occur on a final image. An image forming system using an intermediate transfer member has two transfer processes, which are a transfer process, as primary transfer means, that performs a primary transfer of a toner image from an electrophotographic photoreceptor to the intermediate transfer member, and another transfer process, as secondary transfer means, that transfers the toner image from the intermediate transfer member to a recording material. Since such an image forming system has two transfer processes as described above, degradation of transferability remarkably degrades the quality of final images.
Concretely, if transferability of toners degrades in an image forming system using an intermediate transfer member, a problem that a part of a toner image is not transferred, that is, so-called “hollow defects” or “character blurring” occurs.
For improvement of transferability which may cause “hollow defects” or “character blurring”, prevention of toner filming, and improvement of incomplete cleaning, there has been discussion about technologies that provide micro particles in the surface layer of an electrophotographic photoreceptor, form irregularities on the surface thereof, reduce adhesion force of toner to the surface of the photoreceptor, improve transferability, and decrease friction force against a blade. In TOKKAI No. H05-181291, for example, it is reported that micro particles of alkyl sill sesqui oxane resin are provided in a photoreceptive layer. However, micro particles of alkyl sill sesqui oxane resin are hygroscopic, therefore, in a high moisture environment, wetness of the surface of a photoreceptor, that is, the surface energy increases, accordingly transferability decreases, and a result desired by the inventors is not obtained. In TOKKAI No. S63-56658, an electrophotographic photoreceptor provided with fluoride resin powder to lower the surface energy of the surface of a photoreceptor is reported. However, there is a problem that fluoride resin powder does not achieve enough surface strength, and streak defects due to scratches on the photoreceptor surface easily occur.
On the other hand, regarding improvement of the transferability of an intermediate transfer member, there are disclosed technologies that provide an intermediate transfer member with a solid lubricant to decrease the surface energy of the intermediate transfer member. For example, TOKKAI No. H06-337598, TOKKAI No. H06-332324, and TOKKAI No. H07-271142 disclose such technologies. Also, in TOKKAI NO. H03-242667 for example, there are presented methods in which elastomer is employed as an intermediate transfer member, and the surface roughness of the intermediate transfer member is specified so that the contactability between the intermediate transfer member and a transfer material is improved, thereby improving transferability. Further, in TOKKAI No. S63-194272, TOKKAI No. H04-303869, TOKKAI No. H04-303872, and TOKKAI No. H05-193020 for example, there are also presented methods of specifying the surface roughness of an intermediate transfer member to improve transferability.
However, such a control of the surface of an intermediate transfer member is not enough to improve total transferability of an image forming system using an intermediate transfer member and having two transfer processes. Particularly, when forming copy images in an environment of a high temperature and high humidity or for a long period, it is even less enough to improve “hollow defects” and “character blurring”.
The inventors have discussed about presenting an image forming apparatus and an image forming method which improve transferability of toner in an image forming system, the image forming system using an intermediate transfer member, to prevent image defects such as “hollow defects” and “character blurring”. As a result, regarding image defects of “hollow defects” and “character blurring” described above, the inventors have recognized that the relationship between the water content ratio of an electrophotographic photoreceptor and that of an intermediate transfer member is significantly related to the image defects. The inventors have recognized that image defects such as “hollow defects” and “character blurring” under a high humidity is closely related to the relative magnitude between the water content ratio of an electrophotographic photoreceptor and that of an intermediate transfer member, and if the magnitudes of the water content ratios are different, image defects such as “hollow defects” or “character blurring” easily occur.